Hydraulic lash adjuster

ABSTRACT

A hydraulic lash adjuster ( 1 ) for a valve train ( 16 ) of an internal combustion engine, said hydraulic lash adjuster ( 1 ) comprising a hollow cylindrical housing ( 2 ) and a pressure piston ( 3 ) that are axially inter-inserted for axial displacement relative to each other, a bottom ( 4 ) of the pressure piston ( 3 ) comprising a central passage ( 5 ) for hydraulic medium from a reservoir ( 6 ) enclosed by the pressure piston ( 3 ) into a high pressure chamber ( 8 ) situated between the bottom ( 4 ) of the pressure piston ( 3 ) and an opposing bottom ( 7 ) of the housing ( 2 ), said passage ( 5 ) comprising, on an end ( 9 ) oriented toward the high pressure chamber ( 8 ), a one-way valve ( 10 ) that opens toward the high pressure chamber ( 8 ), wherein a flexible disk-shaped body ( 11 ), that is capable of floating on the hydraulic medium, extends within the reservoir ( 6 ). In this way, a “break-through” of air from the reservoir ( 6 ) into the high pressure chamber ( 8 ) is avoided. During a re-suction process in the lash adjuster ( 1 ), the body ( 11 ), so to speak, follows an air funnel that is being formed in the reservoir ( 6 ) in the direction of the one-way valve ( 10 ).

FIELD OF THE INVENTION

The invention concerns a hydraulic lash adjuster, typically for a valvetrain of an internal combustion engine, said hydraulic lash adjustercomprising a hollow cylindrical housing and a pressure piston that areaxially inter-inserted for axial displacement relative to each other, abottom of the pressure piston comprising a central passage for hydraulicmedium from a reservoir enclosed by the pressure piston into a highpressure chamber situated between the bottom of the pressure piston andan opposing bottom of the housing, said passage comprising, on an endoriented toward the high pressure chamber, a one-way valve that openstoward the high pressure chamber.

BACKGROUND OF THE INVENTION

A lash adjuster of a generic type is disclosed in U.S. Pat. No.6,196,175 B1. This lash adjuster is installed in a switchable rollertappet of a valve train of an internal combustion engine. Through aroller arranged on its housing, the roller tappet is in contact at oneend with a cam. At its other end, the roller tappet acts through asupport of its pressure piston on a tappet push rod.

A drawback of this prior art roller tappet is that its pressure pistonencloses only a relatively small reservoir for hydraulic medium. Duringa re-suction of hydraulic medium during a base circle phase of the camand, thus, a lash adjusting phase of the lash adjuster, the partialvacuum forming in the high pressure chamber causes the hydraulic mediumcolumn to collapse in the shape of a funnel toward the one-way valve.The lower the height of the hydraulic medium column, the more clearlydoes this phenomenon manifest itself. In the worst case, it is possiblefor the air funnel to “sink” completely into the one-way valve. As aresult, an undesired re-aspiration of air into the high pressure chambertakes place. These effects occur more frequently after a longerstandstill of the internal combustion engine because of the emptying ofthe reservoir. Such a “break-through” of air into the high pressurechamber is, however, also encountered in so-called “taxi operation” ofthe internal combustion engine, i.e. during an extreme short-distanceoperation of the engine.

The undesired accumulation of air in the high pressure chamber of thelash adjuster, which air, moreover, can only be re-evacuated with someamount of difficulty out of the high pressure chamber, results not onlyin rattling noises but also in wear. Besides this, the air can have adetrimental effect on the gas exchange process.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a lash adjuster of thepre-cited type in which a penetration of air from the reservoir into thehigh pressure chamber can be avoided by simple measures.

This and other objects and advantages of the invention will becomeobvious from the following detailed description.

SUMMARY OF THE INVENTION

The invention achieves the above objects by the fact that a flexibledisk-shaped body, that is capable of floating on the hydraulic medium,extends within the reservoir.

This disk-shaped body is made preferably of a thin-walled plastic. It isclear that to guarantee the floating ability of this body, its densitymust be lower than the density of the hydraulic medium.

The body preferably has a circular geometry. However, it is alsoconceivable to use general polygonal, rectangular or rounded shapes oredge configurations. The claimed flexibility of the body is not anindispensable condition for implementing the invention. If necessary, itis also possible to use a body that is more or less inflexible.

If the inventive body is used and the hydraulic medium columnaccumulated in the reservoir tends to collapse in a funnel-shape in thedirection of the one-way valve, the body follows the funnel that isbeing formed and counteracts this.

A person skilled in the art will choose the geometry and the flexibilityetc. of the body, so that an undesired re-aspiration of air, asdescribed in the introduction, does not take place. Thus, the undesiredeffects such as rattling noises, wear etc. are also eliminated.

According to a further feature of the invention, the body itself mayalso be pre-shaped to have a slight resemblance to a funnel. Thus, inthe case of a possible abutment of the body against the upper side ofthe bottom of the pressure piston, an excellent seal is created for thepassage, to that a re-aspiration of air is prevented.

It goes without saying that a criterion for the choice of the materialof which the body is made is that this material, for example plastic,must be oil resistant and, at the same time, must be able to resist theprevailing oil temperatures.

As mentioned above, according to a further and particularly advantageousfeature of the invention, if the hydraulic medium column in thereservoir happens to sink down completely, the body provided by theinvention guarantees a disk valve-type sealing of the passage at its endoriented toward the reservoir. Because the body is closed at all eventsin the region of its center, at least the re-aspiration of air into thehigh pressure chamber is avoided despite an absence or deficiency ofhydraulic medium in the reservoir.

Preferably, the body extends with its edge near a wall of the reservoir.The body is thus guided by the wall. If necessary, the body may alsocomprise circumferentially spaced recesses starting from its edge, forexample in the shape of fractional cylinders, so that a good transfer ofoil is guaranteed in this region.

According to a further feature of the invention, the lash adjuster isinstalled, for instance, in a switchable or non-switchable rollertappet. The undesired phenomenon of re-aspiration of air into the highpressure chamber can be encountered particularly in switchable elementsbecause of their restricted design space conditions and the resultingrelatively small reservoir in the pressure piston.

The measures of the invention are conceivable and intended for use inmany types of hydraulic lash adjusters, for example, also in suchadjusters as are installed in cup tappets or support elements or aredesigned as insert elements for lever-type cam followers, or for use inany type of hydraulic length compensators in valve trains, in belt orchain tensioners or the like. If the case arises, any oil foam that maybe formed can also be “squeezed away” by means of the inventive body.

The invention will now be described more closely with reference to theappended drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a tappet push rod drive of an internal combustion enginecomprising a roller tappet, in a schematic representation,

FIG. 2 is an enlarged representation of the lash adjuster comprising apressure piston, showing an initial stage of formation of an air funnelin the reservoir of a lash adjuster during re-aspiration of air,

FIG. 3 shows the undesired “break-through” of the air funnel in thedirection of the one-way valve,

FIG. 4 shows a disk-shaped body of the invention floating on arelatively low hydraulic medium column in the reservoir, and

FIG. 5 illustrates the sealing of the passage to the high pressurechamber by the disk-shaped body.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 discloses a valve train 16 that is represented in the presentcase as a tappet push rod drive. A roller tappet 15, shown in thisfigure in a partial longitudinal section, comprises a housing 2 that isinter-inserted with a pressure piston 3. This pressure piston 3 isdesigned for axial displacement relative to the housing 2 and enclosesin its interior, a reservoir 6 for hydraulic medium (see also succeedingfigures). The drawing shows the reservoir 6 only partially filled withhydraulic medium.

The reservoir 6 communicates with a high pressure chamber 8 situatedthereunder through a passage 5 in the region of a bottom 4 of thepressure piston 3. In the direction leading away from the reservoir 6,the high pressure chamber 8 is likewise defined by a bottom 7. Thisbottom 7 must not necessarily form a part of the housing 2. On a side 9turned away from the reservoir 6, the bottom 4 comprises a one-way valve10, configured in the present case as a ball valve. The one-way valve 10opens in a known manner toward the high pressure chamber 8.

As described in the introductory part of the description, when theamount of hydraulic medium accumulated in the reservoir 6 isinsufficient, it is possible (s. FIG. 2) that, during a re-suction ofhydraulic medium into the high pressure chamber (keyword: lash adjustingphase during cam base circle), an air funnel develops in the directionof the one-way valve 10. In the worst case, as shown more closely inFIG. 3, this air funnel can even break through to the one-way valve 10,so that, in an extremely undesired manner, air penetrates into the highpressure chamber 8.

At this point, the measures of the invention, that can be implementedvery economically, become effective. To prevent the aforesaid undesired“break-through” of air in the direction of the high pressure chamber 8,it is proposed to let a disk-shaped body 11 float on the hydraulicmedium column in the reservoir 6. The body 11 preferably has a flexibleconfiguration and advantageously extends with its outer peripheralsurface at a slight distance from a wall 14 of the reservoir 6, so thatits centered positioning is assured. If the hydraulic medium columnshows a tendency to form a funnel during re-suction, the center of thethin, flexible body 11 follows, so to speak, this funnel, so thatre-aspiration of air is effectively prevented.

In the case of an almost complete absence of hydraulic medium in thereservoir 6, the body 11, as disclosed in FIG. 5, can also serve as adisk valve-like seal of the passage 5 at the upper end 12 of thispassage 5. Thus, a re-aspiration of air into the high pressure chamber 8is avoided under all circumstances.

1. A hydraulic lash adjuster, typically for a valve train of an internalcombustion engine, said hydraulic lash adjuster comprising a hollowcylindrical housing and a pressure piston that are axiallyinter-inserted for axial displacement relative to each other, a bottomof the pressure piston comprising a central passage for hydraulic mediumfrom a reservoir enclosed by the pressure piston into a high pressurechamber situated between the bottom of the pressure piston and anopposing bottom of the housing, said passage comprising, on an endoriented toward the high pressure chamber, wherein a flexibledisk-shaped body, that is capable of floating on the hydraulic medium,extends within the reservoir.
 2. A lash adjuster of claim 1, wherein ifa hydraulic medium column in the reservoir sinks to a level of a bottomof the reservoir, the body forms a disk valve-type seal of the passageat an end of the passage oriented toward the reservoir.
 3. A lashadjuster of claim 1, wherein the body is pre-shaped, so that wheninstalled, the body has an at least slightly convex or funnel-shapedgeometry in direction of the passage.
 4. A lash adjuster of claim 1,wherein the body is made of plastic.
 5. A lash adjuster of claim 1,wherein an edge of the body extends one of near a wall or on a wall ofthe reservoir.
 6. A lash adjuster of claim 1, wherein the body comprisescircumferentially spaced recesses that start from an edge of the body.7. A lash adjuster of claim 5, wherein the body comprisescircumferentially spaced recesses that start from the edge of the body.8. A lash adjuster of claim 1, wherein the lash adjuster is one ofinstallable or installed in one of a switchable or a non-switchableroller tappet.